Recently, with increasing demand for small and high output light emitting apparatuses, demand for large flip-chip type light emitting devices and vertical light emitting devices having high heat dissipation efficiency and applicable to such high output light emitting apparatuses also increases. Since the flip-chip type or vertical light emitting device includes an electrode directly bonded to a secondary substrate, the flip chip type or vertical light emitting device has much better heat dissipation efficiency than a lateral light emitting device. Thus, since such a flip chip type or vertical light emitting device can effectively transfer heat towards the secondary substrate even upon application of high density current, the flip-chip type and vertical light emitting devices are suitable for a light source for high output light emitting apparatuses.
On the other hand, a typical nitride-based light emitting device is fabricated by growing a nitride-based semiconductor layer on a growth substrate having the c-plane as a growth plane, such as a sapphire substrate. However, since the c-plane as the growth plane has polarity in a direction in which electrons and holes are combined, spontaneous polarization and piezoelectric polarization occur in a grown nitride-based semiconductor layer. Such a polarization phenomenon deteriorates internal quantum efficiency of the light emitting device, thereby causing efficiency droop. In addition, a sapphire substrate used as the growth substrate has low thermal conductivity, thereby reducing heat dissipation efficiency of the light emitting device and causing deterioration in lifespan and luminous efficacy of the light emitting device. Such a typical light emitting device suffers from more significant deterioration in efficiency during operation at high current.
In order to overcome such problems, a light emitting device is fabricated using a non-polar or semi-polar homogeneous growth substrate. Efficiency deterioration due to spontaneous polarization and piezoelectric polarization can be minimized by growing non-polar or semi-polar nitride semiconductors on the homogeneous substrate. A nitride-based semiconductor has non-polar planes including an a-plane ({11-20}) and an m-plane ({1-100}), and various light emitting devices fabricated by growing nitride-based semiconductors on the m-plane non-polar substrate are disclosed in the related art.
However, a non-polar nitride-based semiconductor layer grown on the m-plane as the growth plane exhibit different growth characteristics, optical characteristics, etching characteristics, and the like than a non-polar nitride-based semiconductor layer grown on the c-plane as the growth plane. Particularly, in order to improve light extraction efficiency, a surface treatment technique applied to a semiconductor layer grown on the c-plane is difficult to apply to a semiconductor layer having a non-polar or semi-polar growth plane.